In a manufacturing sequence of a semiconductor device, there is performed a film forming process of forming a nitride film such as a silicon nitride film (SiN film) as an insulating film on a semiconductor wafer (substrate) represented by a silicon wafer.
Conventionally, plasma chemical vapor deposition (CVD) has been widely used as a method of forming an SiN film. Meanwhile, an SiN film by an atomic layer deposition (ALD) method which can form a film at a low temperature and with uniform and good coverage and which has good electric characteristics is also used. As a method of forming an SiN film by the ALD method, conventionally, it is known that a dichlorosilane (DCS) gas as an Si raw material gas and an NH3 gas as a nitriding gas are alternately and repeatedly supplied with a purge process interposed between the supply of the DCS gas and the supply of NH3 gas to form an SiN film, in a batch-type vertical film forming apparatus capable of processing a plurality of semiconductor wafers in a batch.
When forming an SiN film by the ALD method using the batch-type vertical film forming apparatus, a process of firstly supplying a dichlorosilane (DCS; SiH2Cl2) gas to a semiconductor wafer as a substrate using, for example, the DCS gas as a raw material gas and an NH3 gas as a nitriding gas to chemically adsorb Si of a single atomic layer, a process of purging the DCS gas with an inert gas, a process of supplying plasma of the NH3 gas to nitrify the adsorbed Si, and a process of purging the NH3 gas with an inert gas are performed such that an SiN unit film having one molecular layer thickness is formed under predetermined film forming conditions. The processes are repeated by a predetermined number of times, to obtain an SiN film having a predetermined film thickness.
As an application of the SiN film, there may be a sidewall (spacer) in a double patterning technique capable of obtaining a fine pattern less than the resolution limit of photolithography technique. In the aforementioned double patterning technique, an SiN film is formed on an amorphous silicon pattern and then etched so that the spacer (SiN spacer) of the SiN film remains only on a sidewall portion of the amorphous silicon pattern. Thereafter, the amorphous silicon pattern is removed to form a pattern of the SiN film.
In such double patterning, according to further miniaturization of a pattern, the SiN spacer is required to have very severe uniformity and low temperature film formation, and high coverage performance or the like is also required. Therefore, the SiN film by the aforementioned ALD method has been studied.
However, the SiN film generally has high tensile stress, and bending due to the attraction between spacers is becoming a problem as the SiN spacer becomes thinner according to miniaturization of a device.
The SiN film by the plasma CVD method can adjust the stress in the film by adjusting the hydrogen concentration or composition in the film by a gas ratio, a pressure, or the like.
However, the SiN film formed by the ALD method is very dense and has fewer impurities than impurities in the SiN film formed by the plasma CVD method, and it was difficult to control the stress in the film in the required low temperature film formation. Such a stress problem in the film occurs not only in the double patterning spacer but also in the SiN film by the ALD method.